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63 lines
1.5 KiB
C
63 lines
1.5 KiB
C
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#include <tommath.h>
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#ifdef BN_MP_PRIME_FERMAT_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
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*/
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/* performs one Fermat test.
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*
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* If "a" were prime then b**a == b (mod a) since the order of
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* the multiplicative sub-group would be phi(a) = a-1. That means
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* it would be the same as b**(a mod (a-1)) == b**1 == b (mod a).
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*
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* Sets result to 1 if the congruence holds, or zero otherwise.
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*/
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int mp_prime_fermat (mp_int * a, mp_int * b, int *result)
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{
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mp_int t;
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int err;
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/* default to composite */
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*result = MP_NO;
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/* ensure b > 1 */
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if (mp_cmp_d(b, 1) != MP_GT) {
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return MP_VAL;
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}
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/* init t */
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if ((err = mp_init (&t)) != MP_OKAY) {
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return err;
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}
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/* compute t = b**a mod a */
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if ((err = mp_exptmod (b, a, a, &t)) != MP_OKAY) {
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goto LBL_T;
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}
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/* is it equal to b? */
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if (mp_cmp (&t, b) == MP_EQ) {
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*result = MP_YES;
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}
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err = MP_OKAY;
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LBL_T:mp_clear (&t);
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return err;
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}
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#endif
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/* $Source: /cvs/libtom/libtommath/bn_mp_prime_fermat.c,v $ */
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/* $Revision: 1.3 $ */
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/* $Date: 2006/03/31 14:18:44 $ */
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